WO2003034581A2

WO2003034581A2 - Method for operating an electronically commutated motor, and motor for carrying out one such method

Info

Publication number: WO2003034581A2
Application number: PCT/EP2002/008802
Authority: WO
Inventors: Alexander Hahn; Walter Heydrich; Hermann Rappenecker
Original assignee: Ebm-Papst St. Georgen Gmbh & Co. Kg
Priority date: 2001-10-10
Filing date: 2002-08-07
Publication date: 2003-04-24
Also published as: DE10246382A1; WO2003034581A3; US20040251863A1; ATE461551T1; US6982534B2; DE50214293D1; EP1413044B1; EP1501184A1; EP1413044A2

Abstract

The invention relates to a method for operating an electronically commutated motor (10) which is provided with a current limiting device acting on a PWM control system (56). During operation, said control system emits PWM pulses (60) with a controllable pulse duty factor (pwm) and an essentially constant frequency. In the event of a pre-determined upper limiting value (Inom; Iw) of the motor current (Iactual) being exceeded, the pulse duty factor (pwm) is modified by means of the current limiting device in order to reduce the motor current (Iactual). In the event of the motor current (Iactual) exceeding a pre-determined upper limiting value (Inom; Iw) during the rotation of the motor (10), said limiting value (Inom; Iw) is increased (fig. 8: Iwmax) during a pre-determined time span (304) using a timer (260), and the available motor power is thus temporarily increased when a peak load occurs. When the rotor (24) is blocked, the limiting value (Inom) is not increased, but rather significantly reduced. The limiting value (Inom) is preferably increased according to the rotational speed of the motor (10), in order to utilize the better motor cooling system during high rotational speeds. The limiting value (Inom) is momentarily increased to a high value when the motor is started (10), in order to enable a reliable start.

Description

Method for operating an electronically commutated motor, and motor for carrying out such a method

Electronically commutated motors are used for many drive tasks, e.g. in vacuum cleaners, device ventilators, medical devices, recording devices for video, etc. There are many demands on such motors, among which a low price comes first. This means that such a motor must be used well for the respective drive task without being overloaded.

This is usually accomplished by limiting current, i.e. the motor current is limited so that it cannot exceed a predetermined upper limit. The power of such a motor is then unnecessarily limited when starting, where a particularly high motor power is necessary. Some such motors could also be operated at higher speeds with higher power, because then their cooling would be better and such a motor could take up and deliver a higher power. Also, such a motor could temporarily temporarily give a higher power at a peak load because it has a "thermal reserve", i.e. if an overload occurs briefly, the motor will not immediately overheat. There are special circuits for this, with which an engine is "simulated" by an electronic or mechanical model, but such solutions are too expensive for low-cost applications.

It is therefore an object of the invention to provide a new method for operating an electronically commutated motor and a new electronically commutated motor for carrying out such a method.

According to a first aspect of the invention, this object is achieved by the subject matter of claim 1. If a load peak occurs in such a motor, so that the motor current exceeds its predetermined limit value, this limit value is increased during a predetermined period of time by a timer, provided that Motor rotates. In this way, the available power of the engine is temporarily increased during a peak load. However, it is preferably avoided that this increase also occurs when the engine is blocked, because in this case it should the motor current should be as low as possible to avoid overheating and the resulting fire risk. - Preferred developments of such a method are the subject of claims 2 and 3. A motor for performing this method is the subject of claim 10.

Another solution to the problem is the subject of claim 4. Because at least one current pulse is generated and supplied to the voltage divider, the current flowing to the voltage divider increases during the duration of this current pulse, and thereby the upper limit of the current increases. This enables a better utilization of the motor, especially when speed-dependent current pulses are generated, which increase the upper limit of the current with increasing speed. This is because an engine is usually cooled better with increasing speed and can therefore output more power. This applies particularly to external rotor motors. - A motor for performing such a method is the subject of claim 11.

A further solution to the problem is the subject of claim 7. The capacitor, which is connected in parallel with a partial resistor of the voltage divider, is discharged before the motor is switched on. Immediately after switching on, it acts like a short circuit for this partial resistor and therefore temporarily increases the upper limit value at start, namely until this capacitor has charged. In this way, the starting torque can be increased in such a motor without this resulting in a permanent overload of the motor. - A motor for performing such a method is the subject of claim 12.

Another solution to the problem is the subject of claim 8. In such a motor, the output signals of the rotor position sensors have a relatively low frequency, which is proportional to the speed of the motor. The invention succeeds in increasing this frequency, specifically in such a way that from zero speed, where the increased frequency also has the value zero, a signal is available whose frequency is increased, for example in the case of a three-phase motor the factor 3, which enables, for example, a more precise display of the speed, a more precise speed control, a more precise detection of the rotational position of the rotor, and a more precise adaptation of the upper limit value of the motor current to the current speed. This means that expensive encoders can often be dispensed with.

A preferred development of the invention according to claim 8 is the subject of claim 9.

The invention is particularly advantageous for electronically commutated external rotor motors.

Further details and advantageous developments of the invention result from the exemplary embodiment described below and shown in the drawing, which is in no way to be understood as a restriction of the invention, and from the subclaims. It shows:

1 is an overview circuit diagram to explain the invention,

2 shows an example of a full-bridge circuit for a three-strand motor,

3 shows a circuit for generating a signal 50 with a speed-dependent frequency, the frequency of which is three times as high as the frequency of the Hall signals of the motor, from which the signal 50 is derived.

4 is a diagram for explaining the mode of operation of FIG. 3,

5 is an overview showing several preferred components working together,

6 is a circuit diagram showing more details of the arrangement of FIG. 5, 7 is a schematic illustration which shows an example of the change in the upper limit Isoii for the motor current as a function of various operating parameters,

8 curves which show the increase in the upper limit of the current with increasing speed for the exemplary embodiment specified; the lower curve Iw shows the speed-dependent increase in this upper limit, and the upper curve Iwmax shows the speed-dependent increase in the upper limit, to which an additional increase is superimposed by activation of an arrangement which is designated by 260 in FIGS. 5 and 6,

9 is a diagram for explaining the mode of operation of the PWM generator 56 of FIGS. 5 and 6,

10 is a representation analogous to FIG. 9, which shows the processes in the case of a temporary increase in the upper limit of the current,

11 is a circuit diagram showing a variant of the arrangement according to FIGS. 5 and 6, and

FIG. 12 is a diagram for explaining the mode of operation of FIG. 11.

In the following description, parts that are the same or have the same effect are designated with the same reference symbols and are usually described only once.

1 shows an overview circuit diagram with an electronic commutated motor (ECM) 10, here as an example a motor with three strands 12, 14, 16 in a delta connection with the connections 18, 20, 22, and a permanent magnetic rotor 24. The latter is an example shown four-pole. It controls three Hall generators 26, 28, 30, which have angular distances of 120 ° el. And generate three signals H1, H2, H3 during operation, which according to FIGS. 4A-4C are each 120 ° out of phase with each other. These signals are used to measure the speed and to control the currents through the strands 12, 14, 16. The ECM 10 is preferably an external rotor motor.

The signals H1, H2, H3 are fed to a signal processor 36 which is shown in FIG. 3 and whose output signals are fed via a schematically illustrated connection 38 to an output stage 40 which is shown in FIG. 2 and a control logic for the control of the currents in strands 12, 14, 16 contains. The connections 18, 20, 22 are connected to the output stage 40. The latter is connected to an operating voltage + UB, e.g. B. to +24 V, +48 V, +60 V or the like. And it is connected via a current measuring resistor 42 to ground 44. The entire current of the motor 10 flows through the resistor 42, which is denoted by list, that is to say the actual value.

A voltage drop occurs across the resistor 42 during operation, and this is fed to a device 46 which limits the current list and serves as dynamic motor protection. A desired rotational speed (rated speed) nsoii for the motor 10 can be set on this device via a potentiometer 48.

The device 46 is supplied with a signal 50 via a line 52, which has three times the frequency of the signals H1, H2, H3 and is produced in the signal processor 36.

Via a signal connection 54, an output signal from the device 46 is fed to a PWM controller 56 which, depending on the signal at the

Connection 54 provides a PWM signal 60. This has a frequency f of z. B.

25 kHz corresponding to a period T = 0.04 ms. This signal 60 has a

Duty cycle pwm of pwm = t / T ... (1), which is between 0 and 100%, depending on the size of the signal at input 54.

The signal 60 is fed to the output stage 40 via a connection 62. The device 46 preferably has the basic function customary in such motors, to regulate the speed to a desired value, e.g. B. to 10,000 rpm, and limit the motor current list to a predetermined value, which according to FIG. 8 at 10,000 rpm z. B. is about 4.2 A.

When starting, the device 46 should briefly apply the current, e.g. B. during 0.5 s, limit to a higher value, as shown in FIG. 7 or 12 z. B. to 7 A.

If higher loads occur for a short time, the device 46 should absorb these load increases by z. B. allows a higher current of 5.5 A for one second, even at the start, between these higher currents (5.5 A) there should always be sections with "normal" current of 3.5 A, which sections z. B. last 4 s.

And finally, when the motor 10 is blocked, that is to say at the speed 0, the current is to be reduced to a low value, for. B. to 1.3 A, so that the motor 10 is not overheated at standstill.

Furthermore, according to FIG. 8, the permissible current Isoii (Iw in FIG. 8) for an external rotor motor 10 should increase with the speed n, because in particular an external rotor motor is better cooled with increasing speed and therefore "tolerates" a higher current when it is at a higher level Speed running.

Naturally, all of these functions do not have to be implemented in a particular motor 10, but can only be partially used, and the numbers given are only examples to facilitate understanding.

Fig. 2 shows the essential elements of the power section 40. This contains a full bridge circuit with three upper transistors 70, 72, 74, which are designed as P-channel MOSFETs, and three lower transistors 76, 78, 80, which is an N-channel -MOSFETs are formed. A free-wheeling diode 70 ', 72', 74 ', 76', 78 ', 80' is connected antiparallel to each of these transistors. In the case of the upper transistors 70, 72, 74, the source S is connected to + UB via a line 82. In the case of the lower transistors 76, 78, 80, the source S is connected to a bus 84, which is connected to ground 44 via the measuring resistor 42, so that the full motor current flows via the resistor 42.

The drain connections D of the transistors 70 and 76 are connected to the winding connection 18 of the motor 10, the D connections of the transistors 72 and 78 to the winding connection 20 and the D connections of the transistors 74 and 80 to the connection 22 , B. the transistor 70 and the transistor 78 are conductive, a current flows from left to right through the strand 12 and a smaller current through the series connection of the strands 16 and 14. The level of these currents depends essentially on the voltages in these strands can be induced by the rotating rotor 24 (FIG. 1).

The individual transistors 70 to 80 are switched on via AND gates. For example, according to FIG. 4, between 0 ° el. And 60 ° el. H1 = 1, H2 = 1, H3 = 0, or abbreviated HS = 110.

In this case, the transistors 72 to 80 are controlled as follows:

Transistors 70, 74, 76, 78 = 0

Transistors 72, 80 = 1

This is done via the AND gates shown in FIG. 2. In the

Combination H1 = 1 and H3 = 0, transistor 80 is turned on, and at

Combination H2 = 1 and H3 = 0, transistor 72 is switched on. The others

Transistors remain blocked.

Likewise, between 60 ° el. And 120 ° el. HS = 101.

In this case, transistors 70 and 78 are turned on and the rest

Transistors 72, 74, 76 and 80 are blocked. In this way, the switching state of the full bridge circuit 70 to 80 is switched on after 60 ° el., So that the winding phases 12, 14, 16 generate an electromagnetic rotating field in a known manner, as is common practice in such motors.

For this purpose, in transistor 70 the gate G is connected via a resistor 88 to line 82 and via a resistor 90 to the collector of an npn transistor 92, the emitter of which is connected to ground and the base of which is connected to the output of a resistor 94 AND gate 96 is connected, which outputs a positive signal at its output (and thereby makes the transistors 92 and 70 conductive) when a signal H1 = 1 at the input 98 of the AND gate 96 and a signal H2 / = at the input 100 1 (corresponding to H2 = 0).

In the same way, the transistor 72 is turned on by an AND gate 102 if the values H2 = 1 and H3 = 0 are present on the latter 102.

And the transistor 74 is controlled by an AND gate 104 when the signals H3 = 1 and H1 = 0 are present there. '

The lower transistor 76 is turned on by an AND gate 106 with three inputs when H2 = 1, H1 = 0 and (on line 62) the PWM signal 60 = 1, i. H. the PWM signal 60 switches on and off the lower transistor 76, 78 or 80 which is currently being turned on by the combination of the signals H1, H2, H3.

An AND gate 108, which is activated by H2 = 0, H3 = 1 and PWM signal 60 = 1, is used to control the transistor 78, and an AND gate 110, which is activated by H3 = 0, is used to control the transistor 80. H1 = 1 and PWM signal 60 = 1 is activated.

The commutation according to FIG. 2 is only one example for better understanding of the Invention.

FIG. 3 shows the circuit 36 for forming the signal 50 with three times the frequency of the signals H1, H2, H3. It is particularly advantageous about this circuit that it is effective down to speed 0 and that, by tripling the frequency, a better measurement of the speed of motor 10 and an optimal adaptation of the current limitation to the current speed of this motor is possible.

As shown in FIG. 3, the current inputs of the three Hall generators 26, 28, 30 are connected in series. The upper current input of the Hall generator 26 is connected to a line 122 (e.g. +5 V) via a resistor 120, and the lower current connection of the lower Hall generator 30 is connected to ground 44 via a resistor 124. The resistors 120, 124 are preferably approximately the same size.

A comparator 126 is assigned to the Hall generator 26, to whose two inputs 128 (+) and 130 (-) the two outputs of the Hall generator 26 are connected. The output 132 of the comparator 126 is connected to the positive line 122 via a pull-up resistor 134, to the input 128 via a resistor 136 and to the negative input 140 of a comparator 142 via a resistor 138.

3, the Hall generator 28 has a comparator 126 'and the Hall generator 30 has a comparator 126 ". The circuit is the same in each case and therefore the same reference numerals are used, for example 128, 128' and 128". , and these parts are not described again.

The positive input 144 of the comparator 142 is connected to line 122 via a resistor 146 and to ground 44 via a resistor 148.

The output 150 of the comparator 142 is through a resistor 152, the one Switching hysteresis, connected to the input 140, causes a resistor 154 to lead 122 and a resistor 156, a node 158 and a resistor 160 to ground 44.

The base of an npn transistor 162 is connected to node 158, the emitter of which is connected to ground 44 and the collector of which is connected to an output 164, from which a pulse train can be taken at a frequency which is proportional to the instantaneous speed nist of motor 10 ,

Preferred values for FIG. 3 k = kOhm; M = MOhm comparators 126, 126 ', 126 ", 142. 4 x LM 2901 resistors 120, 124. 200 ohm resistors 136, 136', 136". 220 k resistors 134, 134 ', 134 ", 154,. 3.3 k resistors 138, 138', 138", 146, 148, 156. 33 k resistor 152. 1 M resistor 160. 10 k

Operation of Fig. 3

The two resistors 146, 148, which are of the same size, set the input 144 of the comparator 142 to approximately +2.5 V.

4 H1 = 1, H2 = 1, H3 = 0 in the range 0 ... 60 ° el. Consequently, the output of the comparator 126 "is at ground, and the outputs of the comparators 126, 126 'are not present Ground so that a current flows from line 122 to point 140 via resistors 134, 138 and 134 ', 138' and from there via resistor 138 "to ground 44. 4D, this results in a potential of approximately two thirds of the voltage U = 5 V at point 140, and the comparative comparator 142 receives a high signal at its output 150, which is denoted by 1 in FIG. 4E. 4, H1 = 1, H2 = 0, H3 = 0, ie the outputs of the comparators 126 ', 126 "are at ground, and the output of the comparator 126 has a high resistance. A current now flows from line 122 via resistors 134, 138 to point 140 and from there via resistor 138 'to ground, likewise via resistor 138 "to ground. 4D, this results in a potential of approximately one third of the voltage U = 5 V at point 140, and the comparison comparator 142 consequently receives a low signal at its output 150, which is denoted by 0 in FIG. 4E.

In this way, the potential at output 150 jumps either from 0 to 1 or from 1 to 0 after 60 ° el. The signal 50 is obtained there, the frequency of which is three times the frequency of the signals H1 etc. This signal is also available at exit 164, e.g. B. for monitoring the speed of the engine 10. Such monitoring is required by many customers.

Fig. 5 is an overview for explaining the principles of the invention. The voltage across the measuring resistor 42 is fed via a resistor 207 and a smoothing capacitor 208 to the minus input 210 of a comparator 204, the output of which is designated 216. The plus input 212 of the comparator 204 is connected to a node 214, the potential of which determines the upper limit of the current in the motor 10, that is to say its available power. If this upper limit is exceeded, the pulse duty factor of pulses 60 which are generated by a PWM generator 56 is automatically reduced.

The node 214 is connected to ground 44 via a resistor 240, to a node 232 via a resistor 238, and to the switch 286 of a timing element 260 via a resistor 300, which is connected via a capacitor 262 to the output 216 of the comparator 204.

The node 232 is connected to the line 122 via a resistor 234 and a capacitor 236 parallel to this. Furthermore, he is over a resistor 230 is connected to the collector of a pnp transistor 226, the emitter of which is connected to the line 122 and a speed-dependent signal f (n) is supplied to the base thereof.

The output 216 is connected via a resistor 202 (with the value R2) to the input of the PWM generator 56, which is also supplied with a speed-determining signal "n-signal", usually from one, via a resistor 196 (with the value R1) Speed controller or a manual speed setting. The resistance value R1 is significantly larger than R2. Typical values are given below from which a preferred ratio of R1 to R2 results.

The PWM generator 56 supplies the PWM signal 60 at an output 190, which is fed to the commutation controller 40 via the line 62 (see FIGS. 1 and 2).

Operation of Fig. 5

As long as the potential U210 at the input 210 of the comparator 204 is lower than the potential U212 at its input 212, the output 216 of the comparator 204 has a high resistance and has no influence on the modules 56 and 260 connected to it. This is the case as long as Motor current list is less than an upper limit value, which is predetermined by the potential U212 of point 214.

This potential is in turn determined by the ratio of resistors 234, 238, 240 and by a speed-dependent current 248, which flows via transistor 226 and resistor 230 to node 232, the potential at point 232 being smoothed by capacitor 236. The potential U212 at point 214, and consequently also the upper limit of the current list, therefore increase with increasing speed.

If the current list becomes too large, the comparator 204 tilts and its output 216 is connected to ground 44. The potential change occurring on Output 216 is transferred to the timer 260 via the capacitor 262 and switches on the switch 286, for example for one second, so that the resistor 300 is connected in parallel with the resistors 234, 238 and the potential U212 of the point 214 is raised during this second is, so that the output 216 of the comparator 204 immediately becomes high-resistance again and the current can increase further. After this second the switch 286 opens and the potential U212 at the node 214 drops again, as a result of which the current list is again limited to a lower value. If output 216 is connected to ground, a current flows from input 194 through resistor 202 and comparator 204 to ground 44, which suddenly reduces the potential of input 194. This also immediately reduces the pulse duty factor pwm (equation 1) of the PWM signal 60 in order to reduce the motor current list and to keep it below the desired upper limit. The frequency of the signal 60 remains unchanged, which is an important advantage.

So that the increase in the potential at point 232 and thus also at point 214 is as large as possible, resistor 234 is preferably chosen to be substantially larger than the sum of resistors 238 and 240. The voltage loss across the current measuring resistor 42 is kept as small as possible. Thus, the potential value U212 at point 214 for the current upper limit Isoii is small, and by connecting the resistor 300 in parallel, the current upper limit Isoii can easily be doubled if desired.

At the start, the capacitor 236 is discharged and then acts as a short circuit of the resistor 234, so that at the start the potential U212 of the node 214 is raised until the capacitor 236 has charged. As a result, the starting current of the motor 10 can be greatly increased for a short time in order to ensure a reliable start, as shown at 252 in FIG. 7. A longer lasting increase is possible with the variant according to FIGS. 11 and 12.

An important aspect of the present invention is therefore the voltage divider 234, 238, 240, which, depending on motor parameters, signals different from the outside Type are supplied to optimally utilize or limit the available power of the engine 10. Naturally, the various external influences described on this voltage divider are only examples of the many possibilities that this principle offers.

FIG. 6 shows details of a preferred embodiment of FIG. 5. The same reference numerals are used for the same or equivalent parts as in FIG. 5 as there. The PWM generator 56 contains a triangular generator with a comparator 170, the positive input 172 of which is connected to the line 122 (+5 V) via a resistor 174, to the output 178 via a resistor 176, and to ground 44 via a resistor 180. The output 178 is connected to the line 122 via a resistor 181 and to the minus input 184 via a resistor 182, which is also connected to the minus input of a comparator 186 and to a ground 44 via a capacitor 188. The PWM signal 60 is generated at the output 190 of the comparator 186. The output 190 is connected to the line 122 via a pull-up resistor 192.

The comparator 170 with its various switching elements generates a delta voltage U184 (see FIG. 9) with z. B. 25 kHz at the input 184, and this is fed to the comparator 186.

The positive input 194 is - as potential u - via the resistor 196 e.g. the output signal of a speed controller 200 is fed, which is only indicated schematically, and via the resistor 202, the input 194 is connected to the output of the comparator 204, which is part of an arrangement for limiting the current.

Via the resistor 207 and the filter capacitor 208, the voltage at the measuring resistor 42 determined by the motor current list is fed to the minus input 210 of the comparator 204, as already described in FIG. 5. Its plus input 212 lies at the node 214, and the potential U212 there determines the current Isoii at which the current limiting arrangement is activated: If the potential at point 214 is high, the current becomes limited to a high value and it is low to a low value.

If the current list becomes so high that the potential U210 of the input 210 becomes higher than the potential U212 of the input 212, the comparator 204 tilts and its output 216 goes to ground potential, so that a current through the resistor 194 from the input 194 202 flows to ground, as a result of which the potential U194 at the input 194 of the comparator 186 decreases abruptly, consequently the pulse duty factor pwm of the pulses 60 becomes smaller, and the current list is thereby reduced, since the transistors 76, 78, 80 go out with this pulse duty factor be turned on, as described in Fig. 2.

FIG. 9 shows the triangular voltage u, which is supplied by the comparator 170, which serves as a triangular generator. This triangular voltage is compared in the comparator 186 with the potential U194 at the input 194 of this comparator.

If the motor current list becomes higher than the predetermined value Isoii at the time tio, the comparator 204 tilts, its output 216 goes LOW, and a current flows to the ground 44 via the resistor 202, so that the potential U194 jumps 195 at the time tio downstairs.

As a result, as shown in FIG. 9B, the pulses of the PWM signal 60 become shorter from the time tio, and consequently the motor current list decreases until it is smaller than Isoii again. If this is the case, the comparator 204 switches back to its other state, in which its output 216 is high-resistance, and no current flows through the resistor 202.

A negative change in potential at output 216 causes transistor 264 to turn on and the current upper limit Isoii to increase temporarily, as shown at 304 in FIG. 7, and in this case the length of pulses 60 temporarily increases again.

Control only via the pulse duty factor pwm of the pulses 60 when in use A fixed frequency for the PWM signal 60 is very advantageous since, for example, it is possible to work continuously at 20 kHz or higher. This frequency is outside the human hearing range and the motor 10 becomes quieter.

An arrangement 220 serves to increase the potential at point 214 (cf. FIG. 8) as a function of the speed. Via the series connection of a capacitor 222 and a resistor 224, the pulses 50 (with three times the frequency) are fed to the base of a pnp transistor 226, which via a resistor 228 is connected to line 122 as well as the emitter of transistor 226. The collector of this transistor 226 is connected via a resistor 230 to a node 232, which is connected via a resistor 234 and a capacitor 236 parallel thereto to line 122 (+ 5 V) is connected. Node 232 is also connected to node 214 via a resistor 238, and the latter is connected to ground 44 via a resistor 240.

The resistors 234 (430 k), 238 (100 k) and 240 (8.2 k) form a voltage divider, and in steady-state, when there are no external influences on the voltage divider, ground 44 has a potential of 0 V which Node 214 of 0.076 V, node 232 of 1 V and line 122 of +5 V.

The potential U212 at point 214 determines the current upper limit to which the motor current list is limited, e.g. 8 in continuous operation at 10,000 rpm to about 4.2 A. This potential U212 is fed to the positive connection 212 of the comparator 204, and if it is low, the comparator 204 switches over and already at a low current reduces the potential U194 at the input 194 of the comparator 186, as a result of which the pulse duty factor pwm (equation 1) of the pulses 60 is reduced even when the motor current is low.

Raising the current limit depending on the speed

The arrangement 220 (FIG. 6) generates a current pulse 248 with a constant pulse width for each pulse 50 (FIG. 4E). For the constant pulse duration of the current pulses 248, a particularly advantageous solution is obtained by connecting the base of the transistor 226 to the capacitor 222, the resistor 224 and the resistor 228. The pulse duration results from the product of the value of the capacitance of the capacitor 222 and the sum of the values of the resistors 224 and 228, that is to say C222 * (R224 + R228). The current pulses 248 are supplied to the node 232, so that an additional current 248 flows through the resistors 238, 240 and increases the potential of the point 214. However, this additional current 248 does not flow when the motor 10 is blocked, and this results in a low motor current when the motor is blocked.

Since more pulses 50 and 248 are generated with increasing speed per unit of time, this additional current through resistors 238, 240 increases with increasing speed, so that the current upper limit increases with increasing speed.

So that the potential at point 232 and thus also at point 214 is increased as much as possible, resistor 234 is preferably chosen to be much larger than the sum of resistors 238 and 240.

Dynamic current increase during load surges

An ECM 10 is designed to have a power reserve, i. that is, if he is only asked for an increased output for a short time, this has little influence on his temperature. However, if the same increased power were continuously demanded of the motor 10, this would lead to its overheating and destruction.

For this reason, a dynamic current increase can be used in a very preferred manner in the event of load surges. Part 260 of FIG. 6, the function of which has already been explained in FIG. 5, serves this purpose.

The output 216 of the comparator 204 is connected via a capacitor 262 to the base of a pnp transistor 264, which in turn is connected to the line 122 via a resistor 266. The collector of transistor 264 is connected to ground 44. Its emitter is connected to line 122 via a resistor 268, to a node 272 via a resistor 270, and directly to the minus input 274 of a comparator 276. The node 272 is connected to the via a resistor 278 Plus input 280 of comparator 276 and connected to ground 44 via a resistor 282.

The output 284 of the comparator 276 is connected to the base of an npn transistor 286, further to the line 122 via a resistor 288 and to a node 292 via a capacitor 290, which in turn is connected to the plus input 280 via a resistor 294 and via the series circuit a resistor 296 and a diode 298 is connected to ground 44.

The collector of transistor 286 is connected to line 122, its emitter via resistor 300 to node 214.

If the transistor 286 is conductive, the resistor 300 (180 k) is connected in parallel to connect the resistors 234 and 238 in series, as a result of which the potential U212 jumps to a higher value at point 214 and the current upper limit according to FIG. is raised from 3.5 to 5.5 A.

If the motor current list is too high, the comparator 204 tilts low, and this change in potential is transmitted through the capacitor 262 to the base of the pnp transistor 264 and makes it conductive so that it bypasses the resistors 270, 282 and the comparator 276 switches, which is switched as a monoflop. The transistor 264 suppresses the positive pulses that arise when differentiating through the capacitor 262, so that only the negative pulses can cause the comparator 276 to switch.

The output 284 of the comparator 276 is low in the idle state. If the monoflop is triggered, the output 284 becomes high for as long as is defined by the components 290, 296, 298 and then tilts back to low again.

As long as output 284 is high, transistor 286 is turned on and additional current flows through node 300 and resistor 300 to node 214, as previously described. The transistor 286 acts like an ideal switch, i.e. resistor 300 is decoupled from point 214 when transistor 286 turns off.

The time during which the output 284 is high here is approximately 1 second, and they are each followed by a time of at least 4 seconds in which the output 284 is low, so that, according to FIG. 7, one has short sections 304 with higher current, which are separated from one another by long sections 306 with lower current. This prevents the motor 10 from being overloaded, but permits adaptation to short-term load surges, as can occur with some drives.

When the rotor 24 of the motor 10 is blocked, the current limiting arrangement is constantly active, i.e. H. the comparator 204 is continuously tilted so that no pulses are transmitted via the capacitor 262 and the circuit 260 is not activated.

If the rotor 24 is blocked, no more pulses 50 are generated, so that no more current pulses 248 are generated. The current then drops in accordance with section 308 of FIG. 7 and is limited to a low value 310 at a standstill, so that overheating of the ECM 10 in the blocked state is avoided.

10 shows for FIGS. 5 and 6 a schematic representation of the motor current list, represented by the potential U210 at the input 210 of the comparator 204, and the upper current limit Isoii, represented by the potential U212 at the input 212 of the comparator 204, and the potential U216 at the output 216 of the comparator 204 when the current upper limit Isoii is exceeded.

At time t2o, the upper current limit Isoii is exceeded. As a result, the comparator 204 switches to LOW and the monoflop circuit 260 is activated, cf. Description of Fig. 5, so that the upper current limit Isoii for the time period Ti determined by the monoflop circuit 260, e.g. 1 second, is increased. This makes the potential U216 high again at time t21.

At time t22, the motor current list returned to normal level because, for example, the temporary extra load or fault is no longer present. After the time period Ti, the monoflop circuit 260 is deactivated and the current upper limit Isoii returns to the original value. Up to time t.24, there are no further overruns. At time t24 the upper current limit Isoii is exceeded again and the output 214 is switched to LOW. Since the monoflop circuit 260 does not allow any further increase to protect the motor against overheating after a period of time T2, for example 4 seconds, after the increase in the current upper limit, this has no effect until time 126. The motor current list cannot continue to rise. Between t24 and t26, the potential u216 changes constantly between high and low as shown, since the current limitation to the current value of Isoii is effective here.

In this example, the motor current list falls below the upper current limit Isoii at time t26, and the output 216 goes HIGH again.

At time t28, the upper current limit Isoii is exceeded again. Since the time period T2 has not yet expired, the upper current limit is not increased. This only happens again at time t30, at which time T2 has expired. From t30, the upper current limit Isoii is increased again during the time period Ti. Thus, the motor current list can briefly rise to a higher value, as shown at A.

At time t32, the motor current list drops back into the normal range, and therefore the potential U216 is constantly high again. At time t34, the time period Ti ends and the upper current limit is reduced again to the normal value

5 and 6 is based in part on the fact that the potential U212 at the node 214, which defines the current upper limit, is modified depending on certain operating conditions, so that it either becomes higher or lower and consequently the motor current, depending on the operating parameters of the engine, is automatically limited to different values in order to make the best possible use of the performance of the ECM 10.

FIG. 8 shows an example of the increase in the upper current limit for a motor that is designed for a speed of approximately 10,000 rpm. If the motor is blocked (speed n = 0), the motor current is limited to a value of approximately 1.4 A. The upper current limit Iw = f (n) rises to about 4.2 A at 10,000 rpm. In the upper area, the curve becomes flatter and reaches a plateau, and this flat area is placed near the nominal speed of the motor by selection of the electrical components 222, 224, 228, 230.

8 also shows the curve Iwmax, which corresponds to the increased current upper limit which results from the activation of the monoflop 260. At 10,000 rpm, this increases e.g. the current upper limit from about 4.2 to about 4.8 A, and accordingly the torque M, which is shown on the left scale in FIG. 8 and which is proportional to the actual motor current, increases. Since an external rotor motor is cooled well at 10,000 rpm by the air turbulence generated, it can dissipate much higher heat loss at this speed than at standstill, and therefore the permissible motor current at 10,000 rpm can be significantly higher than with a blocked motor. In this way it is possible to achieve higher speeds and thus higher performance with a motor of a given size.

Within the scope of the invention, it is also possible to temporarily switch off the motor current completely when the motor is blocked and to attempt a new start at regular intervals.

The capacitor 236 at the node 232 smoothes the potential at this point and thus brings about a stable setpoint at the comparator 204.

The arrangement 220 is therefore particularly favorable in the case of external rotor motors, but can of course be used in all motors in which the cooling improves with increasing speed.

Current increase when switching on

The capacitor 236 (1.5 μF) additionally has the function that it is discharged when it is switched on and then acts briefly as a short circuit for the resistor 234. As a result, the potential at node 232 is briefly raised to +5 V, and the potential at node 214 increases to 0.38 V, see above that the current list is limited to a high value. This is shown in FIG. 7 at 252, where after switching on the current limit drops from 7 A to 5.5 A within 0.5 seconds, so that the motor 10 can start with a very high torque, but this is reduced quickly. For the time period T, START of the start pulse approximately applies: tSTART = C236 * R234 * (R238 + R24θ) / (R234 + R238 + R24θ) ... (2)

Preferred values of the components in FIG. 6

Voltage on line 122: +5 V, regulated. Motor with 10,000 rpm nominal speed, k = kOhm, M = MOhm capacitor 222 3.3 nF

Resistor 224, 228 51 k

Transistors 226, 264 BC857

Transistor 286 BC847

Comparators 170, 186, 204, 276 4 x LM2901

Resistor 230 11 k

Resistor 234 430 k

Resistors 180, 238 100 k

Resistor 240 8.2 k

Resistor 42 0.082 ohms

Resistor 206 1 k

Capacitor 208 1 nF

Resistance 196 33 k

Resistors 181, 192, 202, 288 10 k

Capacitor 188 220 pF

Resistance 182 75 k

Resistance 176 33 k

Resistance 174 62 k

Capacitor 262 33 nF

Resistance 266 22 k

Resistance 268 45 k

Resistance 270 3 k

Resistor 282 2 k Resistors 278, 294. 1 M capacitor 290. 1 / F resistor 296. 620 k diode 298. 1 N4148 capacitor 236. 1.5 μF resistor 300. 180 k

FIG. 11 shows a preferred variant of how the speed-dependent signal 50 (FIG. 4E) formed by the circuit 36 (FIG. 3) at its output 150 is fed to the node 232 for a circuit according to FIG. 5 or FIG. 6. This variant differs from FIG. 6 by the two components 231, 233. The other components are largely identical to FIG. 6 and are therefore not described again. The base of the pnp transistor 226 is connected to ground 44 in FIG. 11 via the series connection of a resistor 231 and a capacitor 233.

At start-up, the (previously discharged) capacitor 233 is charged via resistors 228 and 231. The voltage drop across resistor 228 during this charging temporarily makes transistor 226 conductive and thereby switches resistor 230 in parallel with resistor 234, so that the potential at point 232 is raised sharply during this time. The time duration Tstart233 of this increase is approximately the result

Tstart233 = (R228 + R231) * C233 ... (3)

Then, via the resistor 230, the node 232 is supplied with pulses 248 (FIG. 6) with a speed-dependent frequency in order to increase the current upper limit with increasing speed, as described in FIGS. 5 and 6 and shown in FIG. 8. During Tstart233, the value Isoii (which is defined by the potential at point 214) has an increase in the form of a plateau 239 (FIG. 12), which is superimposed on the increase by capacitor 236, and over which a longer start increase in the current upper limit Isoii is reachable. This enables larger inert masses to be accelerated, and the increased current enables a large dynamic starting torque. At the same time, the motor is protected in the event of a blockage, since the transistor 226 is then blocked and the motor current is listed is limited to a small value (see FIG. 7).

Preferred values of the components in FIG. 11

Operating voltage +5 V; k = kOhm

Capacitor 222 ... 1 nF

Resistance 224 ... 200 k

Transistor 226 ... BC857

Capacitor 233 ... 1.5 / F

Resistors 228, 231, 234 ... 430 k

The invention thus relates to a method for operating an ECM 10 which is provided with a current limiting arrangement. This acts on a PWM control, which emits PWM pulses with a controllable pulse duty factor pwm and an essentially constant frequency during operation emitted pulses 60 to reduce the motor current. If, with the ECM rotating, the motor current exceeds a predetermined upper limit Isoii, this limit is increased during a predetermined period 304 (FIG. 7) and thereby the maximum available motor power is temporarily increased during a load peak, usually in the range of a few seconds. If the rotor 24 is blocked, the limit value is not increased, but is further reduced. In a preferred manner, the upper limit value Iw is also increased depending on the engine speed n up to a plateau, as shown in FIG. 8. - The above measures can be used individually or in any combination.

The invention allows the performance of an ECM 10 to be exploited in a very simple manner better than before, without the need for a special (thermal) simulation of the engine. The determination of the upper current limit Isoii (in Fig. 8: Iw) in the speed range of the motor is variable within wide limits. Naturally, numerous other modifications and modifications are also possible within the scope of the present invention.

Claims

claims

1. A method for operating an electronically commutated DC motor which is provided with a current limiting arrangement which acts on a PWM control which, during operation, delivers PWM pulses (60) with a controllable pulse duty factor (pwm) and a substantially constant frequency, which current limiting arrangement if a predetermined upper limit value (Isoii) of the motor current is exceeded, a change in the pulse duty factor (pwm) of the pulses (60) emitted by this PWM control, in order to reduce the motor current, with the following steps:

It is monitored whether the motor current (list) exceeds the predetermined upper limit value (Isoii) of the current limiting arrangement; if the motor current (list) with the motor rotating (10) exceeds the predetermined upper limit value (Isoii), this limit value is increased during a predetermined time period (Ti) in order to make a higher motor power available during this time period.

2. The method of claim 1, comprising the following additional steps: When the current limiting arrangement responds, a signal is generated and transmitted to a timing element which, when activated by this signal, increases the upper limit value (Isoii) of the motor current for a predetermined period of time in order to to make temporary load peaks available by increasing the upper limit value (Isoii) of a higher power of the motor (10).

3. The method according to claim 2, wherein the signal generated when the current limiting arrangement is triggered is transmitted to the timing element via an AC voltage coupling.

4. A method for operating an electronically commutated DC motor which is provided with a current limiting arrangement which is based on a PWM control acts, which in operation PWM pulses (60) with controllable

Duty cycle (pwm) and a substantially constant frequency, which current limiting arrangement changes the duty cycle when a predetermined upper limit value of the motor current is exceeded

(pwm) of the pulses (60) emitted by this PWM controller, in order to reduce the motor current (list), the upper limit being predetermined by a potential at a voltage divider, and the method has the following steps:

Depending on at least one operating condition of the motor, at least one current pulse is generated; this at least one current pulse is fed to the voltage divider in order to increase the upper limit value (Isoll) of the motor current.

5. The method according to claim 4, in which proportional to the speed of the motor (10) current pulses (50) are generated, which preferably have a substantially constant product of time and amplitude and are supplied to the voltage divider in order to speed-dependent the upper limit of the motor current increase.

6. The method of claim 4, wherein a current pulse is generated at start and is supplied to the voltage divider to increase the upper limit of the motor current during the duration of this current pulse (Fig. 11, 12).

7. A method for operating an electronically commutated DC motor which is provided with a current limiting arrangement which acts on a PWM control which, during operation, delivers PWM pulses (60) with a controllable pulse duty factor (pwm) and a substantially constant frequency, which current limiting arrangement if a predetermined upper limit value of the motor current (list) is exceeded, a change in the pulse duty factor of the pulses (60) emitted by this PWM control causes to reduce the motor current (list), the upper limit (Isoii) by a potential at one

Voltage divider is specified, which method has the following steps:

A capacitor becomes parallel to a partial resistor of the voltage divider

(236) is provided which causes an increase in the discharged state and a reduction in the upper limit value (Isoll) in the charged state and which is discharged before the motor is switched on, then essentially like a short circuit for the partial resistance assigned to it

(234) and so when switching on the motor (10) the upper one

Increase limit; after the motor (10) is switched on, this capacitor (236) is charged.

8. Electronically commutated motor (10), which comprises: a rotor (24); a stator with (2n +1) winding phases (12, 14, 16) and (2n +1) rotor position sensors (26, 28, 30) for the delivery of output signals which characterize the instantaneous position of the rotor (24) by their signal combination, whereby n = 1, 2, 3, ...; Each rotor position sensor (26, 28, 30) is assigned a comparator (126, 126 ", 126") provided with an output (132) for processing its output signal, which output (132) has a predetermined first value when a certain value of this output signal is present Accepts potential, and the output of each comparator (126, 126 ', 126 "), via a first resistor (134, 134', 134") with a second potential (line 122) different from the first predetermined potential and via a second resistor ( 138, 138 ', 138 ") is connected to an input (140) of a comparison comparator (142), which is designed to convert the signal (ui4θ) at this input (140) to a signal (U / 2) of a substantially predetermined value Compare size and thereby deliver at its output (150) a signal (50) whose frequency compared to the frequency of the Signal at the output of a rotor position sensor (26, 28, 30) with the engine (10) running is increased.

9. Motor according to claim 8, in which the comparison signal (50) at the output of the comparison comparator (142) is used as a speed-dependent signal.

10. Motor, which is designed to carry out the method according to one of claims 1 to 3.

11. Motor, which is designed to carry out the method according to one of claims 4 to 6.

12. Motor, which is designed to carry out the method according to claim 7.

13. Motor according to one of claims 7 to 11, which is designed as a collectorless electronically commutated external rotor motor.